Drilling Steel

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Sharpening

Make sure that your steel is straight. Bent steel is nearly impossible to use effectively and a poorly placed blow could glance and cause an injury. Keep the steel sharp. Sharp steel helps you work safely and efficiently.

Use a double cut file or grinder to redress steel that is not badly worn. Maintain existing edge bevels as much as possible. In the field file the heads smooth and cutting edges sharp. Use a completed hole as a holder. Insert the steel upside down and brace it with your knee or foot. Your partner may also hold the steel while you file. Always wear gloves when sharpening or holding.

When using a grinder, remember to avoid excessive heating of the steel that could draw temper and soften the bit. Be aware that forged tools are harder on the outside than they are at their core. Careless or excessive grinding or filing can expose the core and cause premature dulling.

Using a hole as a holder.

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One worker may hold the steel while the other files.

Reconditioning and Tempering

The facilities and expertise of a blacksmith will almost certainly be required to completely recondition dull drilling steel. Here is an historical account describing how a blacksmith worked:

"Drills are sharpened, first by forging to the right shape and to give a sharp edge; this edge, however, by many smiths is not hammered sufficiently sharp, and they use either a file or a grindstone to give the required edge. The point is then heated to a glowing red and dipped in cold water for a few seconds to harden the steel; the edge is then rubbed on sand to clean it. The smith examines for the colour, and dips at a pale straw colour to make it hard, or at a dark blue, which makes it a little tougher. If, after the first cooling, there is not sufficient heat in the drill for these colours to show on the edge, it must be reheated in the fire. When the drill is dipped for tempering, it may remain in the water till cold. The exact colour at which steel has to be dipped varies with the quality of the steel, and also, no doubt, with the nature of the work, but a little practice will soon show." (Lupton, 1906).

Special variations in the temper and length of steel were sometimes required to drill particularly hard rock.

Modern hand drilling steel has similar forging requirements. In the reconditioning process it is important for the blacksmith to be able to control the hardness of steel by tempering. In general, the harder the steel, that is, the more cohesive the particles of metal, the more resistant the tool will be to wear. If the steel is made too hard, however, it may become brittle and break during use.

Standards for the hardness of tempered steel have been established that guide smiths to the correct hardness for a tool based on its usual range of applications. Hardness is measured by pressing on tempered surfaces with specific shapes under a known pressure. The amount of pressure that the tempered metal is able to withstand before an indentation is made becomes a measure of its hardness. The best known measures of hardness of tempered steel for tools are Rockwell and Brinell hardness. Rockwell hardness tests measure the indentation of a diamond cone (Rc), or a steel ball of a specified diameter (Rb), on a tempered surface. Brinell hardness tests measure only with a ball (HB) (see Hardness Testing Conversion Table).

The steel on the tool's surface is slightly harder than the steel in the middle. This is because during the quench the particles on the surface are more radically affected; they are more cohesive than those in the middle or slightly beneath the surface. The key to tempering is to retain the desired toughness at the center of the tool. The softer core assures a strong tool, while the hard exterior provides the cutting edge or protective shield.

Drilling Steel continued...